I just got a bonsai from a nursery and after further inspection, I aw that some of the leave had brown spots and others looked like they were being chewed.

What is this and what can I do to stop it?!

Check if it spreads, if it does, then it is most likely a fungus, so spray with a funguside. What species is it? Because you might kill the tree if you spray to much funguside.

. What species is it? Because some spcecies can die if you apply to much funguside.

Looks like natural to me and nothing to worry about. Leaves do die